A widespread public acceptance of aluminum containers, the principal body portions of which are drawn from disk stock using high volume production techniques has led to a concomitant need for reliable, high-speed testing devices. Such testing as carried out by the devices serves to assure the wall integrity of the cans or containers, thus permitting their more predominant usage, the packaging of food products. The presence of defects, for example in the form of pinhole openings or minute cracks, may lead to contamination and spoilage, not only in connection with the contents of defective containers or cans, but also in connection with adjacently packaged containers.
The initial approach utilized in testing the container bodies was one of carrying out pressure testing, for example as disclosed in U.S. Pat. No. 3,750,348 by Masservey et al. While effective, such testing procedures necessarily are slower and require the use of somewhat elaborate machinery. Maintenance costs for the apparatus carrying out air testing are considered to be high as well as is the cost, in and of itself, of pumping air, as well as in the maintenance of rubber pads, air cylinders and the like, all of which are required in the development of a high speed test approach.
Over the more recent past, designers of container testing equipment have looked to the utilization of light as the testing medium, a photoresponsive component being associated with the interior of can bodies, while the exterior surfaces of the cans are flooded with light.
The general approach to providing high speed light testing systems has been to provide a continuously rotating transfer apparatus having successive cradles or pockets within which the can bodies to be tested are deposited in a horizontal orientation, their open ends facing forwardly. An aperture containing wheel corotates with the apparatus, one aperture of a plurality thereof being aligned axially with each can body. As the transfer apparatus rotates, a reciprocally movable holding device which co-rotates with the transfer apparatus and somewhat resembles a piston, contacts the bottom wall of each can body, connects itself thereto through a vacuum port and pushes the can body into the aperture containing wheel in a manner wherein the rim of the can surmounting its open end is urged into contact with a seal at the wheel such that it surrounds an associated aperture. The transfer apparatus continues to rotate and reaches an inspection station whereat all the external surfaces of the can body are illuminated with light of substantially uniform intensity and a photosensitive device positioned within the locus of travel of the can and associated aperture but on the opposite side of the aperture containing wheel is positioned to detect the passage of light through defects within the can body. Upon detecting a defect derived quantum of light within the can body interior, the photoresponsive device develops a signal which is used to discharge the can into a reject channel following further transfer apparatus rotation. Generally, the removal of cans from the transfer apparatus takes place by retracting the holding device while maintaining vacuum connection with the can bottom wall and then terminating the vacuum connection at a proper position, for example at the entrance of a discharge chute. To prevent damage to the can body members as they are urged forwardly and retained against the aperture containing wheel, generally the vacuum holding devices are made yieldable through compression springs or the like. Examples of such devices are revealed in U.S. Pat. No. 3,750,877 by Dvacho et al and U.S. Pat. No. 4,074,809 by McMillin et al.
Another approach to high speed light testing of can bodies is described in U.S. Pat. No. 4,105,122 by Flood et al. In this apparatus, the rotating test carriage is eliminated, the can bodies being fully retained in position by extensible and retractable vacuum connecting holder devices. With the arrangement, the cans are positioned in an in-feed star wheel device and held by vacuum as well as compression against a series of photosensitive stations positioned within a corotating test wheel. Removal of the can body members is by a cooperating discharge star wheel either to a defective can discharge region or to the threshold of a discharge chute. The photosensitive devices used in the testing procedure are designed to provide scrutiny for defects within the can body portion itself as well as in the region of the flange extending from the rim about the open end of the can.
While the above-described testing techniques and associated apparatus represent significant advances in testing technology, improvements looking to the simplification of machinery while maintaining test reliability will be welcomed by industry.